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Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

4i8

ANIMAL FATS—TALLOW

tion numbers, and any other characters which may serve to establish its
origin (see Table XLV).

Animal Fats

The most important animal fats are : butter, dealt with in the chapter
on milk and its products (see Vol. II, Chapter II), tallow, lard, bone-fat
and the foot-oils, which are considered below in detail; a large number
of other fats are obtained from different animals, but few are of importance.
The characters of these are given in Table XLVII.

So-called wool fat, which from its composition is to be regarded as a
wax, is dealt with in the article on waxes.

TALLOW

This is a fat obtained from bovine (ox-tallow) and from ovine animals
(sheep's or goat's fat). It is stiff and yellowish and has a characteristic
smell; in the light and air it rapidly becomes rancid and decolorised. One
part of it dissolves in 40 parts of 94% alcohol. Its physical and chemical
characters are given in Table XLVII.

Its analysis includes firstly the determination of the titer (solidifying
point of the fatty acids), on which depends the commercial value (see T).
Determinations are also to be made of the water and foreign impurities,
of the acid and saponification numbers and, sometimes, of the glycerine
(see General Methods). Any adulteration with bone fat, wool fat, palm oil
or coco-nut oil, may be detected as described below (2).

1. Titer Test.—The sample for this determination must be taken
carefully, portions being taken from each cake or cask (at different points)
of the bulk and these melted together at a temperature not exceeding 60°
and the fused mass continually stirred until it reaches the ordinary tem-
perature.

50 grams of this sample are saponified with 40 c.c. of caustic potash
solution (D 1-4) and 40 c.c. of 96% alcohol. The soap is dissolved in a
litre of water and boiled in a dish to expel the alcohol, the fatty acids being
then separated by means of a slight excess of dilute sulphuric acid and the
boiling continued until these acids form a perfectly limpid layer free from
suspended clots. The aqueous liquid is siphoned off and the acids washed
with hot water until they no longer give an acid reaction with methyl orange
and then solidified by cooling. The disc of solid acids is melted on the
water-bath, filtered through a dry filter in a boiling water-oven and the
filtrate left overnight in a desiccator.

The setting point of the fatty acids thus obtained is ascertained as
foUows : A test-tube b (see Fig. 58) about 15 cm. long and 2 cm. internal
diameter is filled to about two-thirds with the acids (about 30 grams) and
heated in a water-bath until most of the substance is melted ; the tube is
then removed from the bath and the mass stirred with a glass rod until
completely liquid (heating, if necessary, for a few moments). The tube is
then fitted through the hole of the stopper d of a fairly wide glass cylindernifica-